With the development of constructional technologies, modern buildings are getting higher for effective utilization of land. In particular, high-storied business buildings are mainly steel-framed, in which sealed windows are employed, and even if openable windows are employed, the size of the openable windows tends to be small for the purpose of saving the air-conditioning cost of the buildings.
Therefore, in the case of the high-storied business buildings, the artificial air conditioning system is generally employed rather than the natural air conditioning system. The role of a duct serving as an air path for circulating the conditioning air has become more important in the air conditioning system.
According to the related art, the duct, which is essential to the modern buildings, is generally manufactured by bending a galvanized steel sheet in a rectangular shape. In order to increase the strength of the duct, the steel sheet has the thick thickness, so the manufacturing cost for the duct may be increased. In addition, since the weight of the duct is increased, the strength of the buildings must be increased, so the construction cost for the buildings may be increased due to the increase of the strength of the duct.
Further, as the buildings have been built with the large-scale and high stories, the size of the duct must be enlarged. Thus, in order to reinforce the strength of the duct, the thickness of the metal plate for the duct must be increased. However, there are limitations to improve the strength of the duct through the increase in thickness, so the duct is necessarily decreased in length and increased in number as well as reinforcing materials must be used in a great quantity. As a result, the weight of the duct is increased and transportation and construction work for the duct is complicated, so that the overall cost for installing the duct may be increased.
In addition, different from the air conditioning duct, which is concealed by interior and exterior materials of the buildings, the industrial duct is exposed to the outside, so the industrial duct represents the problem in terms of the external appearance as well as the strength.
That is, the metal plate generally used for manufacturing the conventional duct is a simple flat plate or linear beads are regularly formed on the metal plate in the direction vertical to the length direction of the duct in order to improve the strength of the duct. Thus, the aesthetic appearance of the duct may be poor after the duct has been installed.
In particular, the duct employing the flat plate may have a fatality that can hardly absorb vibration from earthquake or machinery.
In this regard, applicant of the present invention has filed an application entitled “an apparatus for manufacturing a metal plate having mesh-type beads for a duct” and this application has been registered as Korean Registered Patent No. 0394557. According to the above application, the metal plate is formed on a surface thereof with regularly intersecting beads so that the duct can be enhanced in strength and vibration applied to the duct can be absorbed at a certain degree by bending portions for forming the beads as well as a regular pattern formed on the surface can provide an effect of improving the external appearance of the duct.
FIG. 8 shows the apparatus disclosed in the above application.
As shown in FIG. 8, the apparatus includes a base frame 41 constituted by a rectangular base plate 41B for settling a driving motor M as a driving unit, four posts 41A respectively erected on four corners of the base plate 41B and an upper plate 41C connected to the upper ends of the posts 41A as an upper part of the base frame 41; a pair of roll stands 42 erected on both ends of the upper plate 41C of the base frame 41; a pair of upper and lower pinch rolls 43 inserted into roll chokes RC by bearings assembled to choke-assembling recesses H at the both roll stands 42; a pair of bead processing rolls 44 assembled to the both roll stands 42 in the same manner parallel with the pinch rolls 43 and having bead-shaped embossments and intaglios in the surface for forming beads; and a power transmission unit constituted by sprockets MS, 43A and 44A respectively arranged at one ends of the rotary axis of the driving motor M, the pinch rolls 43 and the bead processing rolls 44 and a chain C for connecting the sprockets MS, 43A and 44A to drive the bead processing rolls 44 and pinch rolls 43.
The apparatus having the above structure operates as follows.
The sprocket MS provided at the rotary axis of the driving motor is connected to the sprocket 43A provided at one end of the lower pinch roll and the sprocket 44A provided at one end of the lower bead processing roll. Between the lower pinch roll sprocket 43A and the lower bead processing roll sprocket 44A, a tension sprocket TS is rotatably provided at an outer side of the one roll stand for imparting tension to the chain C and ensuring correct and stable power transmission.
Therefore, when the driving motor M is rotated, the lower pinch roll and the lower bead processing roll are rotated together.
In this case, the upper pinch roll is a non-driving roll which is rotated only if contacted with the lower pinch roll, and a sprocket 44C arranged at the other end of the upper bead processing roll is coupled to the sprocket 44B arranged at the other end of the lower bead processing roll so that the upper bead processing roll is driven together with the lower bead processing roll.
In other words, after the driven motor is operated as the interval of the upper and lower pinch rolls is adjusted at or under the thickness of the metal plate, to which the beads are supposed to be formed, the metal plate P is inserted into the roll byte of the pinch rolls and moved into the roll byte of the bead processing rolls 44 by the upper and lower pinch rolls 43 so that the beads are formed in the surface of the metal plate between the upper and lower bead processing rolls having the bead shaped embossments and intaglios to obtain a metal plate DP for the duct.
However, several problems have been found after using the apparatus of the above patent.
First, if the length of the upper and lower bead processing rolls is increased, the center portions of the upper and lower bead processing rolls may be sagged downward due to the weight, so that the formation of beads may be deteriorated.
Second, the metal plate, on which the beads are formed while the metal plate is passing through the upper and lower bead processing rolls, is subject to the density variation due to the formation of the beads, so that the metal plate is gradually bent upward and rolled if the length of the metal plate is increased.
Third, the interval between the upper and lower bead processing rolls must be adjusted according to the thickness of the metal plate. However, if there is an error exceeding the tolerance of the chain and the sprocket, that is, if the interval between the upper and lower bead processing rolls is widened more than the predetermined thickness, the power transmission system is not connected, causing the disable state. Thus, the selection for the thickness of the metal plate may be limited.